C-sections and composite decks formed by cold-formed sheets for a system of composite reinforced concrete columns

ABSTRACT

The present application relates to reinforced concrete columns classed in the category of reinforced concrete according to the NSR-10 and ACI-318 standards, in which the tubular channel is formed by sections with cold-roll sheets (CR) which form C-sections with a core and at least on skid which projects into the inner space of the column, coming into contact with the concrete. The skid comprises along its length a series of perforations through which concrete can pass, allowing a composite column to be formed once the concrete has set, in which steel and concrete work together and mutually strengthen their qualities to such an extent that the thickness of the sheet can be reduced, rendering the product economically viable. Moreover, the invention relates to the composite deck comprising these C-sections and a concrete core confined in the inner space of the tubular channel.

TECHNICAL FIELD

The present application relates to composite reinforced concrete columns, which are classified as reinforced concrete under standards NSR-10 and ACI-318, in which the tubular channel consists of sections made of Cold Roll (CR)-type sheets, forming channel sections having a web and at least one flange projecting toward the internal space of the column, wherein said flange enters in contact with the concrete, and comprises a series of perforations through which the concrete may pass, so that the concrete hardens to form a composite column the components of which work in concert, enhancing the qualities of both steel and concrete, so that the thickness of the steel sheet may be reduced, which makes it possible for the product to be economically viable. Preferably, the channel sections of the present invention are open sections having an “L”, “C”, or “U” shape. Likewise, a part of the present application is an integral and built-in structural system based on said columns.

PRIOR ART

In the construction sector, concrete columns and columns with steel structures are known; columns with sleet structures offer a number of advantages that may be summarized as follows:

-   -   a) Due to the nature of the material, namely steel, the         mathematical analytic models are more representative of the real         models,     -   b) The industrial character of the manufacturing and assembly         processes lead to speed of execution,     -   c) As a result, the final product may reach levels of quality         that are very difficult to achieve when using a material such as         concrete,     -   d) Significantly lower weight of the structural mass, which         translates into lower demands for inertial effects in seismic         events,     -   e) In consequence, lower loads on the soil and consequently on         the foundations,     -   f) 100% recyclable material.

Despite its superior behavior, the spread of steel columns remains at an early stage, particularly in countries such as Colombia with a poorly-developed steel industry, despite the globalization of the economy. One of the causes that explain that fact, arises from the costs.

A widely known and applied alternative is the construction of columns of reinforced concrete and steel, which basically maintains the same construction process that has been applied since it began to be used at the end of the 19th century:

a) Preliminary ironworking: preparation, shaping, and assembly of the reinforcement system;

b) Carpentry: assembly, adjustment and alignment of the mold,

c) Concrete pouring: preparation of the system for working at height, pouring and vibration of the concrete,

d) Waiting time to ensure sufficient setting for removing the mold, and

e) Removing the mold.

That this procedure has been kept almost unaltered for more than one hundred years, apart from revealing the absence of significant improvements, implies that the process conserves two activities that have the nature of a craft, namely the carpentry in wood or metal and the ironworking, with the consequent implications: high labor consumption at the site with higher risk of errors, longer execution times and, consequently, high direct and administrative costs.

Structurally, steel profiling is more efficient for components subject to tensile or flexural stresses. This is not the case for compression or flexural compression demands, which are typical in columns: for these demands, conventional steel profiles, such as I sections, as shown in FIG. 1, are more vulnerable to the phenomenon of torsional buckling, which limits their compressive strength; in contrast, this constraint does not apply to square, rectangular or circular sections, as are typical of columns in reinforced concrete.

Additionally, concrete offers a good compressive strength, at lower costs. The foregoing determines that, for the usual requirements applicable to columns, the alternative using reinforced concrete generally offers lower costs than its current equivalent in steel profiling.

On the other hand, from the structural and functional standpoint, it is observed that, with respect to the reinforcement formed by steel bars, a concrete coating must be provided, which, as specified in title C.1.7.7.1 of the NSR-10 standard, must not be less than 40 mm, the basic function of which is to protect it from corrosive processes and potentially against a conflagration event, as a short-term thermal insulator.

Complementing the function of this concrete coating, in NSR-10 sections C.10.8.2, C.10.8.3, and C.10.8.4, in one of its paragraphs, it is stated: “The basic idea of: C10.8.2, C.10.8.3, C.10.8.4, is that it is appropriate to design a column of sufficient dimensions to withstand the increased load, and then simply add concrete around the designed section, without increasing the reinforcement, so that it is within the minimum percentages required by C.10.9.1. The additional concrete must not be considered to resist loading.” For a square column of 250 mm on a side, the minimum section of covering, namely 40 mm, represents 54% of the total section of the column. More than half of the entire section is not used in terms of compressive strength.

In an attempt to find an option that combines the superior compressive strength of concrete in “full” sections with the superior tensile strength of steel, but also maintains the advantages of quick execution of steel construction systems, eliminating the molding process that reinforced concrete columns require, composite columns have been produced and analytic models and procedures have been defined and systematized in construction standards such as AISC-LRFD, for the use of tubular channels with concrete cores or composite sections that require molding, such as the columns shown in FIG. 1, which are an example of the existing art.

The alternative standard, reflected by the ACI-318 standard and the Colombian equivalent NSR-10, like almost all international standards, replaces the activities of carpentry and ironworking by industrial processes that correspond to the category of composite columns and within these, tubular channels with concrete cores. In this standard, the mold is made up of the tubular channel that in turn fulfills the function of reinforcement, so that the two activities of a handicraft character are merged into one industrial production activity, with the main component being the tubular channel.

The NSR-10 standard, in section C10.13.1, describes the composite sections composed as follows: “ . . . Composite elements subjected to compression must include all those elements that are longitudinally reinforced with structural steel profiles, pipes or tubes with or without longitudinal bars.” Obviously these are closed continuous sections. Later in that section: CR10.13.2 states; “The same rules that are used to calculate resistance, using the load-moment interaction, for reinforced concrete sections may also be applied to composite sections. The interaction diagrams for filled concrete tubes (composite sections) are identical to those of the ACI Design Handbook . . . ” Sections CR.10.13.3 and CR.10.13.4 specify the systems for stress transfer between the core concrete and the steel tubular channel as follows: “ . . . The direct connection may be developed to transfer the forces between the steel and the concrete by means of projections, plates or reinforcing bars attached to the profile or structural tube before placing the concrete . . . ” Section C.10.13.6.1 establishes the minimum thickness values, with the equations reproduced below; the first of said equations is for rectangular or square sections and the second corresponds to circular sections.

In these equations, the variables are e: minimum thickness for the length side; b or diameter; D, f_(y); yield strength of steel, E_(s): modulus of elasticity of steel. So, for example, for a square section with a minimum indicated length of 250 mm, according to the standard f_(y)=413 MPa and E_(s)=200,000 MPa, so the minimum thickness of the wall will be ≈6.55 mm.

$e = {b\sqrt{\frac{f_{y}}{3\; E_{s}}}}$ $e = {D\sqrt{\frac{f_{y}}{8\; E_{s}}}}$

The prior criteria of the standard set out the basics of the application of the columns of composite sections and obviously, their level of development in the present, which severely limit their application for the following economic reasons:

-   -   The definition established in section C10.13.1 states: “pipes or         tubes with or without reinforcing bars . . . ”, refers to         structural tubular channels with wall thicknesses equal to or         greater than 6 mm. It exclusively provides the structural         tubular channel as an option to replace the reinforcing bars,         constitutes a severe economic disadvantage. The cost per unit         weight of the structural tubular channel exceeds that of the         reinforcing bar by more than 40%. The reduction of it         ironworking activity that its use would entail is not enough to         equalize its cost as compared to the reinforcing bars.     -   In addition to the above, the yield strengths of the steel in         reinforcing bars, which are greater than those of structural         tubular profiles, determine larger sections of tubular channels         than those required by the reinforcing bars, and consequently,         higher consumption of tubular steel, with higher unit values         than in the case of reinforcing bars.     -   Likewise, the concept of transferring stress “ . . . through         projections, plates or rebars attached to the structural profile         or tube . . . ” entails an additional cost for this component of         the composite section.     -   In addition to the costs indicated, the requirement is imposed         of treatments for surface protection against corrosion. In the         case of a tubular channel “reinforced” by pillars or columns,         which play a fundamental role in the stability of the structural         system they form, a high degree of surface protection is         required that guarantees its useful life.     -   Although studies carried out in Spain by CIDECT (International         Committee for the Development and Study of Tubular Construction)         in the seventies established that tubular channels filled with         concrete could withstand fire at temperatures on the order of         600° C. for up to 90 minutes, it is necessary to protect the         tubular reinforcement against conflagration events.

In addition to the economic issue, the worldwide use of this type of columns remains very limited because the system does not work efficiently as a composite section; that is, stress transfer between the two components, namely the concrete and the steel tubular channel or encased steel profile, which is essential for the section to have a composite character and for the components to work efficiently in concert, does not occur effectively, because when the concrete sets, due to the nature of the chemical reaction, the concrete retracts and detaches from the internal walls of the tubular channel or the surface of the encased profile, eliminating the direct contact between the two components. The compressive strength of the concrete is disregarded and the solution is not economically efficient.

As an alternative way to ensure a combined effect, the 2010 AISC standard specifies the use of shear connectors to guarantee stress transfer between the concrete and the steel tubular channel or encased profile. On this subject, the AISC-360-10 standard¹ establishes that the “Steel anchors utilized to transfer longitudinal shear shall be distributed within the load introduction length, which shall not exceed a distance of two times the minimum transverse dimension of the encased composite member above and below the load transfer region. Anchors utilized to transfer longitudinal shear shall be placed on at least two faces of the steel shape in a generally symmetric configuration about the axis of the steel section. Steel anchor spacing, both within and outside of the load introduction length, shall conform to Section 18.3e.”¹ AISC-360-10. Chapter I, Section I8, Page 171, related to the “Design of composite section members,” Item 4, “Detailing Requirements,” 4a “Encased composite members” and 4b “Filled composite members.”

In addition to the above, and in relation to “Filled Composite Members,” the AISC-360-10 standard establishes that: “Where required, steel anchors transferring the required longitudinal shear force shall be distributed within the load introduction length, which shall not exceed a distance of two times the minimum transverse dimension of a rectangular steel member or two times the diameter of a round steel member both above and below the load transfer region. Steel anchor spacing within the load introduction length shall conform to Section 18.3e.”

The parameters indicated above introduce higher costs in the column fabrication process, which renders this solution uncompetitive for a high cost input such as tubular profiles.

Among the documents related to this type of column is patent application JPH03144047 by KAWASAKI STEEL CO, which discloses a composite column that improves the transfer of forces between a beam and a pillar, with the support beam being welded to a square steel tube, and the concrete being placed in said steel tube. The system consists of a metal tube (11), square in section, to which beam brackets (12) are welded. The metal tube (11) is filled with concrete (15) through the through holes (14) located on faces of said tube. After the concrete (15) has cured, the through members (14) are locked in place. This arrangement causes dispersion of the tensile force exerted on the brackets (12) and prevents out-of-plane deformation of the side part of the steel tube (11). The beam brackets (12) are bolted to another section.

Another document that relates to a composite system is the patent application KR20120099822, which relates to a method of constructing a prefabricated steel column with reinforced concrete using L-shaped and open steel profiles, so as to remarkably reduce construction time by allowing a panel zone of a PSRC column to absorb a verticality error. In a preferred form of the invention, for L-shaped steel profiles (11) are vertically positioned at the corners of a rectangular cross section. Auxiliary reinforcing bars (12) are added to the gaps between the L-shaped steels and are surrounded by the bars (13). Steel plates (15) are welded to the outer sides of the L-shaped steels and the auxiliary reinforcing bars.

In the prior art, there have been composite columns as disclosed by ACESCO¹, who disclosed a composite column formed by ripen profiles made of steel sheets, of CR or HR type, especially in the form of “C,” which are joined along the joints of the C sections, forming a tubular section encased with concrete. Although such columns are an alternative for steel and concrete columns, their interaction is not strong enough for the column to function as a composite element that has a combined effect. ¹ http://www.aceseo.com/downloads/detalles/Porticos.pdf

Likewise, GERDAU CORSA² offers among its products columns in which the design of the structural members is formed by steel profiles that work conjointly with reinforced concrete elements, or with coatings or fillings of this material. Specifically, it mentions composite columns, formed by steel profiles, rolled or made with sections or plates, bolted or welded, or by tubes or members that have a hollow steel rectangular cross section, encased in or filled with reinforced concrete, and beams or girders, either closed or open-webbed longitudinal members, called “joists”, which are made of steel and are encased in reinforced concrete or supporting a slab, interconnected in such a way that the two materials work in concert. ² http://www.gerdaucorsa.com.mx/articulos/Construccion_Compuesta.pdf

Like ACESCO, GERDAU CORSA relates to a composite column, with a peripheral system of steel sheets, of CR or HR types, which are joined by type 70XX welding along the joints of the “C” sections, with an intermittent weld head, 50 mm per 250 mm, creating an interior space occupied by concrete.

Despite the existence of composite columns with different types of profiles, some of which arc similar to those of the present invention such as those of ACESCO and GERDAU CORSA, all columns with tubular channels and a concrete core require the presence of welded attachments inside the walls of the tubular channel, as provided by the current standard for this category of composite sections, namely NSR-10 sections CR.10.13.3 and CR.10.13.4.

Thus, in the prior art there remains a need for a system of composite columns, the profiles of which act in concert with the concrete, efficiently ensuring stress transfer between the two components, namely the concrete and the tubular channel or steel profile, and achieve sufficient contact to interact with each other so that the compressive strength of the concrete and the tensile strength of the steel work separately, maintaining the advantage of rapid execution of steel construction systems while remaining economically cost-effective.

In summary, I-shaped encased composite systems are very expensive, and circular or square systems require shear bolts that are distributed along the length of the column. Consequently, existing systems

-   -   are not viable because the required minimum thickness to be         categorized as a composite column is 4.8 mm, which increases         costs because it is much more expensive than rods.     -   Steel on the exterior entails treating the steel to prevent         corrosion and so forth, such as with resins or other expensive         materials. Galvanized is not used because the sheet thickness         required according to the standard is very expensive. The column         defined herein allows the thickness of the sheet to be reduced         sufficiently to permit using galvanized steel or stainless         steel.     -   Additionally, said columns require welds to join the bolts or         projections that increase the quantity of material and time         required for their construction.

DESCRIPTION OF THE DRAWINGS

FIG. 1. Illustrates examples of composite columns of the prior art having steel profiles of different shapes, such as H-shaped, circular or rectangular with an interior space filled with concrete.

FIG. 2A. Shows a cross section of an L-shaped composite channel section according to the present application.

FIG. 2B. Shows a cross section of a C-shaped composite channel section according to the present application.

FIG. 2C. Shows a cross section of a U-shaped composite channel section according to the present application.

FIG. 3A. Shows a side view of an L-shaped composite channel section according to the present application.

FIG. 3B. Shows a side view of a C-shaped composite channel section according to the present application.

FIG. 3C. Shows a side view of a U-shaped composite channel section, according to the present application.

FIG. 4A. Shows a top view of the column of the present invention, consisting of four L-shaped composite channel sections (1A) and four C-shaped composite channel sections (1B), where the flanges of components A and B have been joined and the concrete has set within the internal space thereof.

FIG. 4B. Shows a top view of the column of the present invention, consisting of four shaped composite channel sections (1C), wherein the tabs of components A and B have been joined and the concrete has set within the internal space thereof.

FIG. 5A. Top view of the column of the present invention, consisting of four I-shaped composite channel sections (1A) and four C-shaped composite channel sections (1B), showing the sections of the concrete bridges that pass through the perforations made in the flanges of the composite channel sections.

FIG. 5B. Top view of the column of the present invention, composed of four U-shaped composite channel sections (1C), showing the sections of the concrete bridges that pass through the perforations made in the flanges of the composite channel sections.

FIG. 6. Shows a diagram and the photo of a test conducted on the concrete core.

FIG. 7. Shows a detail of the connection between the composite decking and a pedestal.

FIG. 8. Shows a detail of the connection between the composite decking and a beam.

FIG. 9. Analysis using the finite element method, in the STAAD.Pro V8i program, to simulate the behavior of one of the faces of a composite channel section that is internally restricted by the concrete core. The boundary conditions for the nodes are freedom of movement along the Z axis, which corresponds to the vertical displacement of the body of the column, but impossibility of displacement along the X axis due to the presence of the concrete core.

FIG. 10. Table showing the degrees of freedom that are defined for the lateral nodes.

FIG. 11. Analysis using the finite element method, in the STAAD.Pro V8i program, to simulate the behavior of one of the faces of a composite channel section subjected to the load necessary to bring the section of the sheet to the yield point, the loads being distributed over the lateral nodes of the model as follows: upper half of lateral nodes with loads oriented in the −Z direction. Lower half of lateral nodes with loads oriented in the +Z direction.

The results are shown in the table of FIG. 12. Displacement perpendicular to the plane of the sheet, direction Y, or buckling, is zero.

FIG. 12. Results of analysis of buckling and displacement in X, Y and Z.

FIG. 13. Shows a column-beam connection.

FIG. 14. Shows the anchor length (11).

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to composite channel sections formed from steel sheets, preferably cold-rolled (CR) type steel, characterized in that the composite channel sections comprise a web (1) and at least one flange (2) projecting into the internal space of the column, coming into contact with the concrete (4) and said flange (2) comprises a series of perforations (3) along the length thereof, as shown in FIGS. 2 and 3. These perforations allow the concrete to pass through them before solidifying, and once it sets, a bridge (5) of concrete is formed, marked by circles in FIG. 5, which ensures that a composite column constructed with the channel sections of the invention works in concert, enhancing the qualities of both steel and concrete, so that the thickness of the sheet may be reduced, which makes it possible for the product to be economically viable.

These channel sections are produced in galvanized steel or stainless steel the thickness of which fluctuates between 0.45 mm and 3 mm. In contrast, the existing prior art provides equivalent composite section solutions with tubular channels of greater thickness or compact section and stress transfer devices in the form of attachments that require welding, which ultimately results in an increase in costs; as a result, said columns are not commonly used because they are not cost-effective.

The aforementioned channel sections (1) are L-shaped (see FIGS. 3A and 4A), C-shaped (see FIGS. 3B and 4B) or U-shaped (see FIGS. 3C and 4C) and have a pair of flanges (2) at each end.

In a preferred embodiment of the invention, the width of the web (1) of the channel sections must be less than 150 mm, the width of the decking (2) is between 50 mm and 75 mm, preferably the flanges (2) have a width of 75 mm, and the perforations (3) are distributed equidistantly along the flange and centered relative to the lateral edges of the flange. They have a diameter that ranges between 25 mm and 38 mm, and preferably, said diameter is 25 mm, the distance (L) between one center of a perforation and another is 1 to 2 times the diameter of the perforations, preferably said distance of separation is 75 mm and the distance between the center of the perforation (3) and the edges of the flange (2) is 37.5 mm.

Likewise, part of the present application is an integral and built-in structural, system based on said channel sections for the construction of composite columns.

Said composite columns are formed by composite decking comprising different combinations of the channel sections of the present invention. To form the tubular channel, the flanges (2) of the channel sections are temporarily joined by means of an adhesive of the epoxy resin type or 70XX welding type, so that the perforations (3) of the adjacent flanges coincide to allow concrete to flow through them, and the channel sections create an empty space therewithin to form a tubular section having the dimensions of the column. The definitive union of the channel sections that make up the tubular channel is given after the concrete has been poured into the empty space and has set, by means of clamping by the through sections of the concrete core that pass through the perforations (3), creating a bridge (5) that reinforces the system made up of COMPOSITE CHANNEL SECTIONS-CONCRETE CORE, achieving the connection and interaction required for the composite column to function as such and for the components to act in concert. The transfer of stresses between the core and the composite channel sections will then be given by the shear strength of the sections of the concrete bridges that pass through the perforations (3) and remain encased in the concrete core, as shown in FIGS. 5A and 5B.

In the case of the steel sheets with “L”, “C” or “U” shapes in FIGS. 2 and 3, to ensure balanced combined action of the concrete and the section of steel sheet, it must be the case that: When the concrete (2) that passes through the perforations, fails due to shear, the sheet steel (1) will be entering into yield, thus taking advantage of the maximum capacity of each component in the section.

In a preferred alternative embodiment of the invention, the tubular channel of the column comprises four L-shaped composite channel sections (1A), located at the corners, joined to four C-shaped composite channel sections (1B) that occupy the central part, as shown in FIG. 5A. In another embodiment of the present invention, the tubular channel comprises four U-shaped composite channel sections (1C), as shown in FIG. 5B.

However, the integrated construction structural system of the present application also includes the concrete core. In one embodiment of the invention, the mixture design for the concrete core will be for a compressive strength of 40 MPa.

In a preferred embodiment, the concrete mixture has a water/cement ratio=0.4; comprises a superplasticizer additive, a water-reducing additive based on modified polycarboxylates or the like; has a consumption of 16 mL/kg of cement; and includes a coarse aggregate such as crushed stone, with a maximum size of 15 mm, and metallic fibers of circular cross-section with anchor hooks on their ends, classification I, ASTM A820-11, these fibers having a diameter of 0.75 mm±0.03 mm, a length of 60 mm±0.03 mm and a minimum tensile strength of 1,100 MPa. Metal fiber consumption ratio: 160 kg/m3.

For concrete with that proportion of metallic fiber, it is indispensable to conduct laboratory tests to determine its shear strength, which increases with the proportion of this aggregate. Test standard for shear: JSC SF-6. FIG. 6 shows a diagram and photo of a test. In said test, the specimen is a beam of 500 mm×150 mm×150 mm and the test is pure shear, which gives a conservative result in the case of elements subjected simultaneously to compression, such as the one that corresponds to the present development. The study “ENERGY OF FRACTURES IN MODE II OF CONCRETE OF NORMAL RESISTANCE REINFORCED WITH SHORT STEEL FIBERS”, conducted by engineers Fabián Augusto Lamus Báez and Sergio Mauricio Segura Arenas, page 166, see Appendix: 1, establishes that the concrete qualifies for a shear strength of: 15.46±0.65 MPa, which is the strength of the concrete used in the columns of the present invention.

Finally, the construction method comprising the following steps is part of the subject matter of the invention disclosed herein;

a. Making the channel sections in L and C shapes or a U shape, depending on the type of column desired;

b. Temporarily joining the flanges (2) of the channel sections by means of an adhesive or welding, guaranteeing that the perforations (3) of the adjacent flanges coincide, so as to leave a hollow space through which the concrete may flow, and creating an empty space inside the channel sections that are joined to form the tubular channel;

c. Filling the interior space of the tubular channel with concrete; and d. Waiting for the concrete to set, so that upon solidifying, the through sections of the concrete core that pass through the perforations (3) generate bridges (5) that permanently join the channel sections and consolidate the composite column of COMPOSITE CHANNEL SECTIONS-CONCRETE CORE.

EXAMPLES Example 1 Construction Details

COMPOSITE COLUMN-FOUNDATION PEDESTAL JOINT: Applies to both reinforced concrete and steel structures. As shown in FIG. 7, the structural connection is given by the extension of the first reinforcing section of the column (6) rising from the pedestal (7), for a length not less than the development length (61) of the bar of greater diameter inside the concrete core (4) of the composite section (6). Said column (6) is attached to the pedestal (7) by means of leveling nuts (71), adjusting nuts (72) and anchor bolts (73). The base plate frame (8) fulfills only the function of facilitating the positioning of the composite decking.

JOINT BETWEEN COMPOSITE COLUMN AND BEAMS OR SLABS: Applies to reinforced concrete structures, specifically plates or slabs (9). As shown in FIG. 8, the structural connection is given by the extension of the last and first reinforcing section (62) of the column (6) immediately following, for a length not less than the development length (61) of the bar of greater diameter inside the concrete core of the composite section of the consecutive columns formed by the composite decking (63).

JOINT BETWEEN COMPOSITE COLUMN AND BEAMS OR SLABS: Applies to steel structures. FIG. 8 shows that the structural connection is given by through bars that join the steel beams in line. As in the previous case, the column (6) is attached to the plate (9) by means of leveling nuts (91), adjusting nuts (92) and anchor bolts (73).

Example 2 Analytical Basis of Development and Advantages

DESIGN CRITERIA: Standards: ACI-318-11 and NSR-10, Chapter: “Columns of Composite Section,” and AISI standard with respect to COMPOSITE CHANNEL SECTIONS.

STEEL OF THE COMPOSITE CHANNEL SECTIONS: As defined above: Cold Roll sheet of ASTM A572 galvanized steel with thicknesses: 0.45 mm-2 mm or Stainless 302, with thicknesses between: 0.5 mm-1.5 mm. For the analysis, the AISI standard for cold formed steels applies. This regulation, in sections A3.2 and A3.3 relating to DUCTILITY, establishes the applicable criteria for other steels than carbon steels, one of which is Stainless Steel 302 CR.

COMPATIBILITY OF DEFORMATIONS: For the ASTM A572 and Stainless Steel CR 302 and the concrete with the mixture design specifications defined above, the equivalence of the maximum unit deformations within the elastic range is maintained: 0.2%. This is a fundamental hypothesis in the behavior of the composite system.

MINIMUM THICKNESS OF THE COMPOSITE CHANNEL SECTIONS: The applicable standard is AISI B.1.1 “FLANGE FLAT WIDTH TO THICKNESS CONSIDERATIONS: w/t”, which is oriented to ensuring that the section reaches yield before local deformations occur. Additionally, the composite channel section sheet is severely impeded from deforming the interior, because that space is occupied by the concrete core. This is corroborated analytically using the FINITE ELEMENTS method in the STAAD.Pro V8i program, to simulate the behavior of one of the faces of a COMPOSITE CHANNEL SECTION that is internally restricted by the concrete core.

In the example analysis shown below, a thin ASTM A36 steel sheet is modeled having yield strength; 250 MPa or 2549 kgf/cm², with a thickness of 0.6 mm, width of 200 mm, by length 2480 mm, which corresponds to a typical side of a composite channel section. The boundary conditions for the lateral edge nodes (10) are: freedom of movement along the Z axis, which corresponds to the vertical displacement of the body of the column, due to the effect of the compressive load. But displacement along the X axis is impossible, due to the presence of the concrete core and without considering the Poisson effect, which will occur in the final failure phase of the concrete core, see FIG. 9, icons in red-green, which correspond to the support, see right frame: Supports-Whole Structure. The table in FIG. 10 shows the degrees of freedom defined for those lateral nodes. The lower supports of the model in blue, see FIG. 9, are similar to articulations, with freedom of rotation, but impede the vertical displacement of these nodes and correspond to the lower end of the column.

The model will be subjected to the load necessary to bring the section of the sheet to the yield point, the load being distributed over the lateral nodes of the model as follows: Upper half of lateral nodes (10) with loads oriented in the −Z direction. Lower half of lateral nodes (10) with loads oriented in the +Z direction. This load condition would be given by the transfer between concrete core and composite channel section, when applying the indicated load on the upper the of the concrete core. See FIG. 11. Once the model is run under the conditions indicated above, the displacement in the Y (buckling) direction is determined in the most required node: the central nodes in the directions X, Y, Z. The results are shown in the table of FIG. 12. The displacement perpendicular to the plane of the sheet, direction Y, or buckling, is zero.

According to the results obtained:

(C _(F)) Yield load=2549 kg/cm²*20 cm*0.06 cm=3058.8 kgf

Number of lateral nodes: 250

(F) Absolute value of load applied per node=3058.8 kg/250=12.2352 kgf≈12.24 kgf

The above data, using the mathematical finite element model, reveals that “buckling” does not occur in the thin sheet of the tubular or composite decking, working under the restrictions imposed by the concrete core which allow the use of thin sheet as material for the tubular channel of the present invention, which the currently effective NSR-10 or ACI standard does not allow.

STRESS TRANSFER BETWEEN COMPOSITE CHANNEL SECTIONS AND THE CONCRETE CORE: This transfer, together with the hypothesis defined in section 4.2 (COMPATIBILITY OF DEFORMATIONS), allows the two components of the composite system, namely COMPOSITE CHANNEL SECTIONS and concrete core, to work jointly or in concert, preventing one component from sliding relative to the other, as defined above. The model of stress transfer between the two components was previously defined in the following terms: “The stress transfer between the concrete core and the COMPOSITE channel sections will be given by the shear strength of the concrete bridges (5) that pass through the 25 mm-diameter perforations (3) made in the flanges (2) of the composite channel sections, which would be encased in the concrete core.” To take full advantage of the strength of both components, it must be ensured that the concrete bridges are contained within a section of a reasonably short length that we refer to as anchor length (L_(a)) (11), ensuring that none of the components of the composite channel sections will slide before the yield point is reached. For this verification, as an example, the anchor length (11) of a composite channel section will be determined: L 125 mm×1 mm Stainless Steel, which has a higher yield strength than ASTM A572 steel CR galvanized sheets. See FIG. 14,

Perimeter of section L125×1: p=2 (125 mm+75 mm)=400 mm

Diameter of concrete through sections: D=25 mm

Area of concrete through sections: A_(c)=πr²=π12.5² mm²=490.86 mm²

Anchor Length: L_(a)

Number of sections that work against shear for each through section:2

Anchor Length: L _(a)=76 mm+25(n−I)

Effective area of section L125×1: A _(es)=(400 mm−2×25 mm)×1=350 mm²

Yield limit of Stainless Steel CR 302: 1.308 MPa

Maximum stress of the steel section when it reaches the yield point: T_(s)

T _(s)=350 mm²×1.308 MPa=457.800 N

Concrete shear strength: v_(c)=15.46 MPa

Maximum tension of the concrete through sections: T_(c)

T _(c)=2n 490.86 mm²×15.46 MPa=n 15,177.4 N

Accordingly, n=457,800.0 N/15,177.4 N=30

L _(a)=76 mm+25(30−1) mm=801 mm

In conclusion, the composite decking of the present application offers the option of fabricating the tubular channel on site from CR sheets, which facilitates the construction operation, from transportation, to storage, to the construction process that incorporates the assembly of the tubular channel, to the fabrication of the mold.

On the other hand, the thickness of the sheets used in the composite decking of the invention ranges between 0.45 mm and 3 mm, which is much, lower than the minimum thickness required for existing systems in the prior art, which must be greater than 6 mm. Additionally, the location of the thicknesses of the open sections may vary according to the quantitative requirements of the column section: this is not possible in conventional tubular channels having uniform wall thicknesses.

Another relevant advantage of the present invention is that costs may be reduced by not requiring additional components that must be welded, such as projections, plates or reinforcing bars attached to the profile or structural tubing before placing the concrete.

In addition to the foregoing, the characteristics of the concrete core ensure the necessary shear strength that is provided by the combined action of the two parts, the steel tubular channel and the concrete core. Additionally, the option of producing the channel sections in galvanized sheet steel or stainless steel, allows implementing two alternatives for protection against corrosive processes, depending on the aggressiveness of the corrosive medium.

Finally, the open section sheet in stainless steel 302. makes it possible to fabricate the tubular channel with steel having a yield strength of 1138 MPa, which requires smaller quantities as compared to the 4.12 MPa of the reinforcing bars or the 345 MPa of ASTM A572 galvanized sheet steel. 

1. A composite channel section formed from a steel sheet, comprising: a web; and p1 one or two flanges projecting into the internal space of the column, coming into contact with the concrete, said flanges comprising: a series of perforations with a diameter ranging between 25 mm and 38 mm; and a distance between a center of one perforation and an adjacent perforation, the distance being 1 to 2 times the diameter of the perforations.
 2. The composite channel section of claim 1, wherein the steel sheet is a Cold Roll (CR) type sheet.
 3. The composite channel section of claim 2, wherein the channel sections are produced in galvanized steel or stainless steel.
 4. The composite channel section of claim 1, wherein the thickness of the sheet ranges between 0.45 mm and 3 mm.
 5. The composite channel section of claim 1, having an L, C or U shape and a pair of flanges at each end.
 6. The composite channel section of claim 1, wherein the width of the web of the channel sections is between 1 mm and 150 mm.
 7. The composite channel section of claim 1, wherein the width of the flanges is between 50 mm and 75 mm.
 8. The composite channel section of claim 7, wherein the flanges are have a width of 75 mm.
 9. The composite channel section of claim 1, wherein the perforations are distributed equidistantly along a length of the flange, and are centered relative to the lateral edges of the flange.
 10. The composite channel section of claim 9, wherein the distance between the center of one perforation and an adjacent perforation is 75 mm and the distance between the center of the perforation and the edges of the flange is 37.5 mm.
 11. A composite decking comprising: a tubular channel comprising: a web; one or two flanges projecting into the internal space of the column, coming into contact with the concrete, said flanges comprising: a series of perforations with a diameter ranging between 25 mm and 38 mm; and a distance between a center of one perforation and an adjacent perforation, the distance being 1 to 2 times the diameter of the perforations; and a concrete core confined in the internal space of the tubular channel.
 12. The composite decking of claim 11, further comprising: four L-shaped composite channel sections, located at the corners, joined by their flanges to the flanges of four C-shaped composite channel sections that occupy a central part; wherein the perforations of the adjacent flanges coincide.
 13. The composite decking of claim 11, further comprising: four U-shaped composite channel sections, joined together via their flanges.
 14. The composite decking of claim 12, wherein the flanges of the channel sections are provisionally joined by means of an adhesive-type epoxy resin or type 70XX welding, generating a vacuum within the same so as to form a tubular channel having the dimensions of the column.
 15. The composite decking of claim 14, wherein the flanges are finally joined through clamping by the sections of the concrete core that passes through the perforations creating a concrete bridge.
 16. The composite decking of claim 11, wherein the mixture for the concrete core has a compressive strength of 40 MPa.
 17. The composite decking of claim 16, wherein the concrete mixture comprises metallic fibers of circular section having anchor hooks at their ends, the fibers having a diameter of 075 mm±0.03 mm, a length of 60 mm±0.03 mm and minimum tensile strength of 1.100 MPa.
 18. The composite decking of claim 17, characterized in that the proportion of metallic fiber in the concrete mixture is 160 kg/m3.
 19. The composite decking of claim 17, wherein: the concrete mixture has a water/cement ratio=0.4; further comprises a superplasticizer additive or a water-reducing additive based on modified polycarboxylates; and has a consumption of 16 mL/kg of cement, and includes a coarse aggregate such as crushed stone, with a maximum size of 15 mm.
 20. A method of constructing composite decking, comprising: making channel sections in L, C, or U shapes, depending on the type of column desired; temporarily joining the flanges of the channel sections by means of an adhesive or welding, guaranteeing that the perforations of the adjacent flanges coincide, so as to leave a hollow space through which the concrete may flow, and creating an empty space inside the channel sections that are joined to form the tubular channel; filling the interior space of the tubular channel with concrete; and waiting for the concrete to set, so that upon solidifying, the through sections of the concrete core that pass through the perforations generate bridges that permanently join the channel sections and consolidate the composite column of composite channel sections-concrete core. 